Scalable lead zirconium titanate (PZT) thin film material and deposition method, and ferroelectric memory device structures comprising such thin film material

ABSTRACT

A novel lead zirconium titanate (PZT) material having unique properties and application for PZT thin film capacitors and ferroelectric capacitor structures, e.g., FeRAMs, employing such thin film material. The PZT material is scalable, being dimensionally scalable, pulse length scalable and/or E-field scalable in character, and is useful for ferroelectric capacitors over a wide range of thicknesses, e.g., from about 20 nanometers to about 150 nanometers, and a range of lateral dimensions extending to as low as 0.15 μm. Corresponding capacitor areas (i.e., lateral scaling) in a preferred embodiment are in the range of from about 10 4  to about 10 −2  μm 2 . The scalable PZT material of the invention may be formed by liquid delivery MOCVD, without PZT film modification techniques such as acceptor doping or use of film modifiers (e.g., Nb, Ta, La, Sr, Ca and the like).

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] This invention relates generally to a novel lead zirconiumtitanate (PZT) material having unique properties and application for PZTthin film capacitors, as well as to a deposition method for forming PZTfilms of such material, and ferroelectric capacitor structures employingsuch thin film material.

[0003] 2. Description of the Related Art

[0004] There is a major effort by semiconductor companies throughout theworld to commercialize high dielectric constant and ferroelectric thinfilms in advanced dynamic random access memories (DRAMs) andferroelectric random access memories (FeRAMs), respectively.

[0005] While the majority of current efforts are directed to thecommercial development of relatively large capacitors (e.g. 5 μm² area),the ultimate goal is to adapt ferroelectric random access memorytechnology for future generations of integrated circuit devices in whichcapacitor areas, cell sizes and operating voltages are scaled downwardas the technology evolves.

[0006] For FeRAM devices, most research is currently being directed toeither ferroelectric SrBi₂Ta₂O₉ (SBT) or Pb(Zr,Ti)O₃ (PZT) thin films.Each material has relative advantages and disadvantages. Pt/SBT/Ptcapacitors, for example, have been shown to have excellent fatigue andretention characteristics, although processing temperatures in excess of750° C. pose integration issues. For PZT, phase-pure thin films can bedeposited at temperatures in the 450-650° C. range, although Pt/PZT/Ptcapacitors are known to suffer from poor fatigue and retention. In theprior art usage of previously known PZT materials, doping and/or oxideelectrodes have been needed to produce satisfactory capacitor electricalproperties.

[0007] Much of the previous work in the field that has established thefeasibility of PZT and SBT for memory applications has focused on filmsthat switch at 3V and above. Given the inexorable trends towards smallercircuit elements and lower operating voltages, it is extremely desirableto achieve high reliability and performance for thin films at lowoperating voltages, especially below 2V.

[0008] Low operating voltage requires a combination of adequately lowcoercive field (E_(c)) and film thickness. SBT films have been shown tohave low E_(c) (≈35 kV/cm) at thicknesses on the order of 140 nm,resulting in coercive voltages of 0.5V. SBT, however, is handicapped bya low value of switched ferroelectric polarization (P_(sw)), typicallyless than 25 μC/cm². Furthermore, the thermal processing (800° C.)required for improvement of thin film properties is considered severeand undesirable.

[0009] Several studies have presented thickness scaling data for PZTfilms as thin as ˜150 nm. See, for example, P. K. Larsen, G. J. M.Dormans, and P. J. Veldhoven, J. Appl. Phys., 76, (4), 1994; and A. K.Tagantsev, C. Pawlaczyk, K. Brooks, and N. Setter, IntegratedFerroelectrics, 4, (1), 1994. These studies have shown that as the filmthickness is reduced, the coercive field increases and the polarizationdecreases. Such effects have been attributed to depletion anddepolarizing phenomena (A. K. Tagantsev, C. Pawlaczyk, K. Brooks, M.Landivar, E. Colla and N. Setter, Integrated Ferroelectrics, 6, 309(1995)).

[0010] The foregoing effects have been considered by the art to beintrinsic to thin film PZT, and thus low voltage and thickness scalingof PZT was discouraged.

[0011] The high ferroelectric polarization and low processingtemperatures of PZT (compared to other materials) provide a compellingmotivation to identify a form of PZT and a deposition process thatallows scaling the material to low operating voltages.

[0012] It would therefore be a major advance in the art, and accordinglyis an object of the present invention, to provide a form of PZT and adeposition process that allows scaling of the PZT material to lowoperating voltages.

[0013] It is another object of the invention to provide a PZT materialthat is scalable in lateral dimensions (i.e. dimensions parallel to thefilm surface) without incorporating in the material acceptor dopants ormodifiers, e.g., Nb, Ta, La, Sr, Ca, etc.

[0014] It is a further object of the invention to provide a PZT materialof the foregoing type, which is useful for ferroelectric capacitors overa broad range of thicknesses, particularly in the range of from about 20to about 150 nanometers.

[0015] A still further object of the invention is to provide a PZTmaterial that is useful for ferroelectric capacitors over a broad rangeof pulse lengths, particularly in the range of from about 5 nanosecondsto about 200 microseconds.

[0016] Other objects and advantages of the invention will be more fullyapparent from the ensuing disclosure and appended claims.

SUMMARY OF THE INVENTION

[0017] The present invention relates generally to a novel lead zirconiumtitanate (PZT) material, as well as to a deposition method for formingPZT thin films of such material, and ferroelectric capacitor structuresemploying such thin film material.

[0018] As used hereinafter, the following terms shall have the followingdefinitions:

[0019] “Remanent polarization,” Pr, is the polarization at zero voltsafter passing through V_(op).

[0020] “Ferroelectric switched polarization,” P_(sw)=P*−P^ , wherein P*is the polarization transferred out of the capacitor traversing fromzero to V_(op) volts when the capacitor starts at P_(r)(−V_(op)), and P^is the polarization transferred out of the capacitor traversing fromzero to V_(op) volts when the capacitor starts at P_(r)(V_(op)). Thepulse length is 0.23 milliseconds. The measuring instrument used todetermine the values hereinafter set forth was a Radiant 6000 unit.

[0021] “Coercive E-field,” E_(c) is the electric field at which thepolarization is zero during a polarization versus voltage hysteresisloop. The E-field frequency is 50 Hertz for this purpose.

[0022] “E_(max)” is the maximum E-field for the hysteresis loop measuredwith E_(max)=3E_(c).

[0023] “Leakage current density,” J, is measured at the operatingvoltage, V_(op), and a step voltage response at 5 seconds.

[0024] “Retention” is the remanent polarization as measured by themethod described in Integrated Ferroelectrics, Vol. 16 [669], No. 3,page 63 (1997).

[0025] “Cycling fatigue P_(sw)” is the ferroelectric polarizationmeasured with a frequency of 0.5 MegaHertz or slower square pulse, at a50% duty cycle, and a capacitor area of ≦10⁻⁴ cm².

[0026] “Dimensionally-scalable PZT” material means a PZT material thatis un-doped and has useful ferroelectric properties for PZT thin filmcapacitors over a range of thickness of from about 20 to about 150nanometers, and with lateral dimensions as low as 0.15 μm and lower, andcorresponding capacitor areas from about 10⁴ to about 10⁻² μm².

[0027] “E-field scalable PZT” material means a PZT material that isun-doped and has useful ferroelectric properties for PZT thin filmcapacitors over the range of film thickness of 20 to 150 nanometers, ata voltage below 3 Volts.

[0028] “Pulse length scalable PZT” material means a PZT material that isun-doped and has useful ferroelectric properties over a range ofexcitation (voltage) pulse length from 5 nanoseconds to 200microseconds.

[0029] “Ferroelectric operating voltage” means a voltage that whenapplied to a PZT thin film in a capacitor causes the material to bedielectrically switched from one to another of its orientational polarstates.

[0030] “Plateau effect determination” means establishing a correlativeempirical matrix of plots of each of ferroelectric polarization, leakagecurrent density and atomic percent lead in PZT films, as a function ofeach of temperature, pressure and liquid precursor solution A/B ratio,wherein A/B ratio is the ratio of Pb to (Zr+Ti), and identifying fromthe plots the “knee” or inflection point of each plot as defining aregion of operation with respect to the independent process variables oftemperature, pressure and liquid precursor solution A/B ratio, andconducting the MOCVD process at a corresponding value of thetemperature, pressure and liquid precursor solution A/B ratio selectedfrom such region of operation, as hereinafter described.

[0031] “Type 1 properties” means, collectively, a ferroelectricpolarization PSW greater than 20 microCoulombs (μC) per squarecentimeter, a leakage current density (J) less than 10⁻⁵ amperes persquare centimeter at operating voltage, a dielectric relaxation definedby J^(−n) log (time) wherein n is greater than 0.5 and a cycling fatiguedefined by P_(sw) being less than 10% lower than its original valueafter 10¹⁰ polarization switching cycles.

[0032] “Type 2 properties” means, collectively, the followingdimensionally scaled properties of ferroelectric polarization, coerciveE-field, leakage current density, retention and cycling fatigue: BasicThickness Lateral property Scaling (t) dimension scaling (l)Ferroelectric P_(SW) > 40 μC/cm² for t > 90 nm P_(SW) > 30 for 1 > 1 μmpolarization P_(SW) > 30 μC/cm² for t > 50 nm P_(SW) > 20 (P_(SW))P_(SW) > 20 μC/cm² for t > 20 nm for1 > 0.05 μm Coercive E_(c) <100kV/cm for t > 50 nm E_(c) < 100 kV/cm E-field (E_(c)) E_(c) <150 kV/cmfor t > 20 nm for 1 > 0.05 μm Leakage J < 10⁻⁵ A/cm² for t > 90 nm J <10⁻⁴ A/cm² current J < 10⁻⁵ A/cm² for t > 50 nm for 1 > 0.05 μm density(J) Retention < 3%/natural log decade (t in < 3%/natural log de- hours)at 150° C., per procedure cade (t in hours) at for t > 50 nm 150° C.,per procedure for 1 > 0.05 μm Cycling < 10% decrease after 10¹⁰ cycles <10% decrease fatigue for t > 50 nm after 10¹⁰ cycles P_(SW) < 10%decrease after 10⁸ cycles for 1 > 0.05 μm for t > 20 nm

[0033] “Un-doped” in reference to PZT film material means that thedopants and modifiers (heterologous atomic species that are added intothe crystal structure of the PZT material and are responsible for theobserved or enhanced ferroelectric properties of the material) arepresent in the material at concentrations of less than 1 atomic percent.

[0034] In one aspect, the present invention relates to a dimensionallyscalable, pulse length scalable and/or E-field scalable ferroelectricPZT material.

[0035] Another aspect of the invention relates to a ferroelectric PZTmaterial having Type 1 and/or Type 2 characteristics.

[0036] In another aspect, the invention relates to a ferroelectric PZTmaterial that has at least one, more preferably at least two, still morepreferably at least three, and most preferably all four, of the Type Iproperties.

[0037] In a further aspect, the present invention relates to aferroelectric PZT material having at least one of the Type 2 propertiesand progressively more preferably having two, three, four or five ofsuch properties.

[0038] The invention relates in another aspect to a ferroelectric PZTmaterial capacitor comprising a ferroelectric PZT material of adimensionally-scalable, pulse length scalable and/or E-field scalablecharacter, and a capacitor area of from about 10⁻⁴ to about 10⁻² μm².

[0039] Another aspect of the invention relates to a FeRAM device,including a capacitor comprising a ferroelectric PZT material of adimensionally-scalable, pulse length scalable and/or E-field scalablecharacter, and a capacitor area of from about 10⁴ to about 10⁻² μm².

[0040] In another aspect, the invention relates to a method offabricating a ferroelectric PZT film on a substrate, comprising formingthe film by liquid delivery MOCVD on the substrate under MOCVDconditions producing a ferroelectric film on the substrate having Type 1and/or Type 2 characteristics.

[0041] A further aspect of the invention relates to a method offabricating a ferroelectric PZT film on a substrate, comprising formingthe film by liquid delivery MOCVD on the substrate under MOCVDconditions including nucleation conditions producing a dimensionallyscalable, pulse length scalable and/or E-field scalable PZT film on thesubstrate.

[0042] Another aspect of the invention relates to a method offabricating a ferroelectric PZT film on a substrate, comprising formingthe film by liquid delivery MOCVD on the substrate under MOCVDconditions including temperature, pressure and liquid precursor solutionA/B ratio determined by plateau effect determination from a correlativeempirical matrix of plots of each of ferroelectric polarization, leakagecurrent density and atomic percent lead in PZT films, as a function ofeach of temperature, pressure and liquid precursor solution A/B ratio,wherein A/B ratio is the ratio of Pb to (Zr+Ti).

[0043] A further aspect of the invention relates to a method offabricating a ferroelectric PZT film on a substrate, comprising formingthe film by liquid delivery MOCVD on the substrate under MOCVDconditions including Correlative Materials or Processing Requirements,to yield a ferroelectric PZT film having PZT Properties, wherein suchCorrelative Materials or Processing Requirements and PZT Propertiescomprise: Correlative Materials or Processing PZT PropertiesRequirements Basic properties: Ferroelectric polarization Film Pbconcentration > threshold level; P_(SW) > 20 μC/cm² operation on A/Bplateau above the knee region, and with temperature, pressure and gasphase A/B concentration ratio defined by plateau effect determinationLeakage current density Film Pb concentration within a range (between J< 10⁻⁵ A/cm² the minimum and maximum) on the A/B at operating voltageplateau, and with temperature, pressure and gas phase A/B concentrationratio defined by plateau effect determination Dielectric relaxationZr/Ti ratio < 45/55 For characteristic J^(−n) Deposition P > 1.8 torr oclog (time), n > 0.5 and J < 1% ferroelectric switching current from0-100 ns. Retention Operation within ranges of temperature, pres-Maintenance of ferro- sure and gas phase A/B concentration ratioelectric properties defined by plateau effect determination(ferroelectric domains) Avoidance of cycling Use of Ir-based electrodesfatigue P_(SW) < 10% decrease after 10¹⁰ cycles E-field scalabilityOperation within ranges of temperature, pres- sure and gas phase A/Bconcentration ratio defined by plateau effect determination Surfacesmoothness Nucleation-growth conditions during film formation withinranges of temperature, pres- sure and gas phase A/B concentration ratiodefined by plateau effect determination Grain size Nucleation-growthconditions during film formation within ranges of temperature, pres-sure and gas phase A/B concentration ratio defined by plateau effectdetermination

[0044] A still further method aspect of the present invention relates toa method of fabricating a FeRAM device, comprising forming a capacitoron a substrate including a ferroelectric PZT material of adimensionally-scalable, pulse length-scalable and/or E-field scalablecharacter, wherein the PZT material is deposited by liquid deliveryMOCVD under processing conditions yielding a ferroelectric film on thesubstrate having Type 1 and/or Type 2 characteristics as suchferroelectric PZT material.

[0045] Other aspects, features and embodiments of the invention will bemore fully apparent from the ensuing disclosure and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0046]FIG. 1 is a graph of film composition (A/B)f as a function ofgas-phase composition (A/B)_(g) for a PZT thin film material, showingthe insensitivity of the stoichiometry to the precursor concentration.

[0047]FIG. 2 is a model data matrix derived for empirically determinedvalues of the logarithm of the leakage current density (Log J), theferroelectric polarization (P_(sw)) and atomic % Pb in the film, as afunction of pressure (P), temperature (T) and solution A/B ratio.

[0048]FIG. 3 is a schematic cross-section of a semiconductor deviceutilizing a stack capacitor configuration.

[0049]FIG. 4 is a plot of TGA data comparing Pb and Ti compounds withZr(thd)₄ and Zr(O-i-Pr)₂(thd)₂.

[0050]FIG. 5 is a plot of current density versus E-field for PZT filmsvarying thickness showing the current density is only weakly dependenton film thickness above ˜125 nm.

[0051]FIG. 6 is a plot of coercive field (E_(c)) versus film thicknessshowing that E_(c) is nearly independent of film thickness.

[0052]FIG. 7 is a plot of a) P_(sw) versus voltage; and b) P_(sw) versuselectric field.

[0053]FIG. 8 is a plot of P*-P^ versus number of cycles for PZT filmsshowing that fatigue is nearly independent of film thickness.

[0054]FIG. 9 is a plot of imprint behavior for PZT films of varyingthickness.

[0055]FIG. 10 shows the test configuration for the shunt method offerroelectric pulse testing.

[0056]FIG. 11 is a plot of test signal and response signal versus timefor a 10 μm×10 μm capacitor tested with a 1 μs pulse.

[0057]FIG. 12 is a plot of Q_(sw) versus pulse length for variousapplied voltages showing Q_(sw) to be independent of pulse length overthe range investigated.

[0058]FIG. 13 is a plot of Q_(sw) versus capacitor dimension showingQ_(sw) to be independent of area over the range investigated.

DETAILED DESCRIPTION OF THE INVENTION, AND PREFERRED EMBODIMENTS THEREOF

[0059] The present invention provides a unique PZT material that isscalable in character and provides major advantages over the prior artin application to the formation and use of PZT in ferroelectric thinfilm capacitor structures.

[0060] In contrast to the PZT materials previously used in the priorart, the PZT material of the present invention is useful forferroelectric capacitors over a wide range of thicknesses, e.g., fromabout 20 nanometers to about 150 nanometers, and a range of lateraldimensions extending to as low as 0.15 μm. Corresponding capacitor areas(i.e., lateral scaling) in a preferred embodiment are in the range offrom about 10⁴ to about 10⁻² μm².

[0061] The foregoing properties provide a dimensional scaling capabilitythat is achievable without PZT film modification techniques such asacceptor doping or the use of film modifiers such as Nb, Ta, La, Sr, Caand the like.

[0062] The novel PZT material of the present invention in one embodimenthas Type 1 properties, viz., a ferroelectric polarization PSW greaterthan 20 μC/cm², a leakage current density J less than 10⁻⁵ A/cm² atV_(op), a dielectric relaxation defined by J^(−n) log(time) wherein n isgreater than 0.5, and a cycling fatigue defined by P_(sw) being lessthan 10% lower than its original value after 10¹⁰ polarization switchingcycles.

[0063] Such PZT material is a substantial advance over the PZT materialsof the prior art lacking such Type 1 properties, and the presentinvention provides a reproducible method of fabricating such material byliquid delivery metalorganic chemical vapor deposition.

[0064] The present invention relates in one aspect to a method todeposit thin film ferroelectric materials by MOCVD utilizing a liquiddelivery technique. This technique affords precise compositional controlby virtue of mixing liquid precursor solutions and flash vaporizingthem. Flash vaporization has the added benefit of preventing unwantedpremature decomposition of the precursor species. Further, tailoredprecursor chemistries may be employed that are compatible for formingthe thin film material because the precursors do not undergo ligandexchange (or they have degenerate exchange) which prevents the formationof involatile species.

[0065] For thin film PZT and related materials, precise and repeatablecompositional control is required in order to produce films of highquality. Physical deposition methods (e.g., sputtering, evaporation) ofthin film deposition are deficient in this regard, as are traditionalapproaches to MOCVD involving the use of bubblers.

[0066] A process therefore is desired for the formation of thin films ofPZT and related materials, which affords compositional control, providesuniformity of the thin film material over large areas, and achieves ahigh degree of conformality on the substrate structure as well as a highdeposition rate. The deposited material should also be free of pinholes,since in capacitive structures and in many other devices, pinholes willresult in an electrically shorted, useless device.

[0067] In accordance with the invention, the metalorganic precursors ofthe component metals of the desired PbZr_(x)Ti_(1-x)O₃ film areintroduced in liquid form, either as neat liquids or dilute solutions ifthe precursor is a liquid at ambient temperature and pressure (e.g., 25°C. and atmospheric pressure) conditions, or if the precursor compositionis a solid at such ambient conditions, then as a solution of theprecursor in a compatible solvent medium. The solvent medium may be ofany suitable type that is compatible with the specific precursorcomposition employed, as is known and understood by those skilled in theart of liquid delivery MOCVD, and may be constituted by single-componentsolvent species, or alternatively by multicomponent solvent mixtures.

[0068] The metalorganic precursors utilized for such liquid deliverytechnique may for example comprise leadbis(2,2,6,6-tetramethyl-3,5-heptanedionate), [Pb(thd)₂], as a Pbprecursor; titaniumbis(isopropoxide)bis(2,2,6,6-tetramethyl-3,5-heptanedionate),[Ti(O-i-Pr)₂(thd)₂], as a Ti precursor; and zirconiumtetrakis(2,2,6,6-tetramethyl-3,5-heptanedionate), [Zr(thd)₄], as a Zrprecursor. Alternatively, the lead precursor may comprise leadbis(2,2,6,6-tetramethyl-3,5-heptanedionate) N,N′, N″-pentamethyldiethylenetriamine, [Pb(thd)₂pmdeta], and the zirconium precursor mayalternatively comprise zirconiumbis(isopropoxide)bis(2,2,6,6-tetramethyl-3,5-heptanedionate),[Zr(O-i-Pr)₂(thd)₂].

[0069] The solvent media used in the liquid delivery MOCVD process ofthe invention may suitably comprise by way of example the solventcompositions that are disclosed in U.S. patent application Ser. No.08/414,504 filed Mar. 31, 1995 in the names of Robin A. Gardiner, etal., and issued on Dec. 8, 1998 as U.S. Pat. No. 5,846,275, U.S. patentapplication Ser. No. 08/484,654 filed Jun. 7, 1995 in the names of RobinA. Gardiner, et al., and U.S. patent application Ser. No. 08/975,372filed Nov. 20, 1997 in the names of Thomas H. Baum, et al., which arecompatible with the specific metalorganic precursors used for formingthe PbZrTiO₃ thin film materials and efficacious in the constituentliquid delivery and chemical vapor deposition process steps. Thedisclosures of the foregoing patent applications and correspondingpatents based thereon are hereby incorporated herein by reference intheir entireties.

[0070] In one preferred embodiment the solvent media is comprised of asolution containing approximately 8 parts tetrahydrofuran (THF), 2 partsisopropanol and one part tetraglyme (parts by volume). In anotherembodiment, such as the case where Pb(thd)₂ is used, one or both of theisopropanol and tetraglyme would be excluded from the preferred solventmedia. Other illustrative multicomponent solvent compositions include asolvent medium comprising octane:decane:polyamine in an 5:4:1 ratio, anda solvent medium comprising octane:polyamine in an 9:1 ratio. Oneparticularly preferred single component solvent medium istetrahydrofuran (THF).

[0071] The liquid precursor composition once formulated is introducedinto a vaporization zone, in which the liquid is rapidly vaporized,e.g., by flash vaporization on a foraminous vaporization element (e.g.,a porous frit element, or a wire, grid or other high surface areastructural element) heated to suitable temperature, to produce acorresponding precursor vapor.

[0072] The precursor vapor then is transported to the chemical vapordeposition chamber, which may for example comprise a CVD reactor ofknown or conventional type. The CVD system may be suitably equipped tointroduce the precursor vapor into the deposition chamber for contactwith a heated substrate, at a temperature that is suitable to effectdeposition of the metal constituents of the vapor onto the substrateelement. For this purpose, the substrate may be mounted on a heatedsusceptor or other substrate mounting structure, with the spent vaporfrom the process being discharged from the deposition chamber andsubjected to further treatment or processing in a known and conventionalmanner.

[0073] Further, the film as deposited may be further processed in anysuitable manner, e.g., by annealing according to a specifictime/temperature relationship, and/or in a specific atmosphere orenvironment, to produce the final desired thin film PbZrTiO₃ material.

[0074] In one embodiment of the present invention, the precursors forthe metal components of the product film are dissolved in a solvent andflash vaporized at temperatures between about 100 to about 300° C. andtransported into the MOCVD reactor with a carrier gas (e.g., Ar, N₂, H₂,He, or NH₃). The resulting carrier gas/precursor vapor mixture then maybe mixed with an oxidizing co-reactant gas (e.g., O₂, N₂O, O₃ ormixtures thereof) and transported to the deposition chamber to undergodecomposition at a substrate heated to a temperature of from about 400°C. to about 1200° C. at chamber pressures in the range of from about 0.1to about 760 torr. Other active oxidizing species may be used to reducedeposition temperature, as through the use of a remote plasma source.

[0075] Investigation in the field of PZT materials research hasestablished the existence of regimes for CVD process parameters in whichthe film Pb composition is insensitive to changes in precursorconcentrations (see, for example, M. De Keijser, P. Van Veldhoven and G.Dormans, Mat. Res. Symp. Proc., Vol. 310 (1993) p.223-234; and J.Roeder, B. A. Vaartstra, P. C. Van Buskirk, H. R. Beratan, “Liquiddelivery MOCVD of ferroelectric PZT,” Mat. Res. Symp. Proc., Vol. 415(1996) p.123-128).

[0076] This characteristic is highly desirable in application to thedesign and optimization of manufacturing processes, and the inventorshave investigated film properties for films deposited over a range ofprecursor concentrations within this self-correcting regime. It has beendiscovered that although the PZT composition remains substantiallyindependent of precursor concentration, the associated PZT filmmicrostructure and properties can vary significantly. Furthermore, theinventors have discovered that proximity to the “edge” of theself-correcting regime is of primary importance rather than proximity tothe stoichiometric composition. This is a significant finding relativeto the prior art conventional wisdom that a few percent stoichiometricexcess Pb is optimal.

[0077] The present inventors have demonstrated that MOCVD processes fordeposition of PZT have the desirable property of the stoichiometry beinglargely insensitive to process conditions over a fairly wide range ofprocess conditions. However, it has also surprisingly been found thatthe properties of deposited films with the same stoichiometriccomposition are not functionally equivalent. The present inventionresolves this incongruity by an approach that identifies processconditions with optimum electrical properties.

[0078] In a primary aspect, the invention relates to a methodology forselection of CVD process conditions that result in PZT films withsuperior properties. The methodology exploits the “A/B plateau effect”to achieve the fabrication of capacitive PZT films whose electricalproperties are congruent with optimum requirements of ferroelectricnon-volatile (NV) memories such as ferroelectric random access memories(FeRAMs). The “A/B plateau effect” is described below, and is based onthe concept that smoothness and grain size can be controlled bymodifying specific nucleation and growth phenomena. The completeensemble of deposition conditions and principles for selectingprocessing parameters, as described hereafter, result in PZT filmproperties that were previously considered by the art to beunachievable, especially low imprint for un-doped PZT, and E-fieldscaling to low thicknesses, e.g., to thicknesses as low as 20 nm.

[0079] The matrix of PZT properties and correlative materials orprocessing requirement(s) for achieving such properties is set out inTable A below. TABLE A Correlative Materials or Processing PZT propertyRequirement(s) Basic properties: Ferroelectric polarization Film Pbconcentration > threshold level; P_(SW) > 20 μC/cm² operation on A/Bplateau above the knee region; the A/B plateau determines 3 processparameters: P, T and gas phase A/B concentration ratio Leakage currentdensity Film Pb concentration within a range (between J < 10⁻⁵ A/cm² theminimum and maximum) on the A/B at operating voltage plateau; A/Bplateau determines 3 process parameters: P, T and gas phase A/Bconcentration ratio Dielectric relaxation Zr/Ti ratio < 45/55 Forcharacteristic J^(−n) Deposition P > 1.8 torr oc log (time), n > 0.5 andJ < 1% ferroelectric switching current from 0-100 ns. RetentionOperation within ranges of P, T Maintenance of ferro- and gas phase A/Bconcentration ratio electric properties determined above (ferroelectricdomains) Avoidance of cycling Use of Ir-based electrodes fatigue P_(SW)< 10% decrease after 10¹⁰ cycles E-field scaling Operation within rangesof P, T Achieving qualitative and gas phase A/B concentration ratiocapacitor performance determined above for films with reduced A/Bconcentration ratio determined above thickness, and at reduced voltagesSurface smoothness Nucleation-growth conditions during film formationwithin ranges of P, T gas phase A/B concentration ratio determined aboveGrain size Nucleation-growth conditions during film formation withinranges of P, T and gas phase A/B concentration ratio determined above

[0080] An illustrative specific process embodiment that may be used inconnection with the Table A process parameters is set out below, as“Process Set A.” As shown, Process Set A utilizes a specific precursorchemistry including precursor reagents and solvent compositions,substrate and barrier layer materials (the barrier layer being depositedor otherwise provided between the substrate and the PZT material layer),to provide an electrical environment suitable for the achievement ofoptimum electrical and performance properties of the PZT material,electrode materials of construction, carrier gas species and oxidantspecies. Process Set A: Process Condition/Material Precursor ChemistryReagents: [Pb(thd)₂, Ti(O-i-Pr)₂(thd)₂; Zr(thd)₄] Solvents:tetrahydrofuran, glyme solvents, alcohols, hydrocarbon and arylsolvents, amines, polyamines, and mixtures of two or more of theforegoing; examples of illustrative multicomponent solvent compositionsare tetrahydrofuran: isopropanol: tetraglyme in a 8:2:1 volume ratioand/or octane:decane:polyamine in a volume ratio of 5:4:1. Electrodesand Barriers Bottom Electrode: Ir bottom electrode on TiAlN barrierlayer on substrate deposition via sputtering using a collimator anddeposition-etch processing Top Electrode: Structures containing Ir andIrO_(x) for top electrode Carrier Gas, Oxidant: Ar, He, H₂ or otherinert or non-adverse carrier gas; O₂, O₃, N₂O, O₂/N₂O, etc. as oxidantmedium Deposition Conditions: Temperature, Pressure, Precursor Ratio:operate to exploit the plateau effect, in combination with appropriategas delivery, oxidizer constituents, ratios, flow rates, liquiddelivery, liquid flow rate, mixing and deposition time Vaporizer:operate the vaporizer of the liquid delivery system to achieve theforegoing process conditions, as appropriate to the specific vaporizerapparatus employed; examples of vaporizer operating parameters that maybe involved include: back pressure, delivery tube ID, frit porosity,vaporizer temperature, gas co-injection, delivery tube/frit composition,and tube/frit installation procedure

[0081] It will be appreciated that the Process Set A elements are by wayof exemplification only, and that the specific precursor chemistries,carrier gas species, device structure layers, etc. may be widely variedin the broad practice of the present invention to achieve a scalable PZTfilm material within the scope of the present invention.

[0082] The thickness of the ferroelectric film material in the practiceof the present invention may be widely varied. A preferred thickness forFeRAM applications is typically in the range of from about 20 to about150 nanometers. Operating voltages for such PZT material films in FeRAMapplications are typically below 3.3 Volts, down to much lower voltagelevels.

[0083] The general formula for perovskite oxides is ABO₃, where specificmetal elements occupy the A and B sites in the crystal lattice, and O isoxygen. For PZT, Pb is on the A site and Zr and Ti share the B site.Because the vapor pressure of PbO is lower when its incorporated in theperovskite structure, fairly wide ranges of CVD process parametersresult in PZT films with the same or very slightly varying A/B siteratio ≈1.00. The existence of this A/B “self-correcting effect” isutilized to advantage in the present invention to achieve the formationof PZT material with the properties of a ferroelectric polarizationP_(sw) greater than 20 μC/cm², a leakage current density J less than10⁻⁵ A/cm² at V_(op), a dielectric relaxation defined by J^(−n)log(time) wherein n is greater than 0.5, and a cycling fatigue definedby P_(sw) being less than 10% lower than its original value after 10¹⁰polarization switching cycles (Type 1 properties).

[0084]FIG. 2 is a model data matrix derived for empirically determinedvalues of the logarithm of the leakage current density (Log J), theferroelectric polarization (P_(sw)) and atomic % Pb in the film, as afunction of pressure (P), temperature (T) and solution A/B ratio.

[0085] Model data from the matrix show the basic relationships betweenthe independent (process variables) P, T and (A/B)_(solution), on thedependent variables: atomic % Pb in the film, ferroelectric polarization(P_(sw)) and leakage current density (log J). Among these variables,(A/B)_(solution) is equivalent to (A/B)_(gas) since the precursor liquidreagent solution is vaporized to achieve a same gas-phase composition asis present in the liquid solution of the precursor.

[0086] Visual inspection of the various curves generated for thedependent variables (including average values for the central and edgeregions of the ferroelectric films in the model data matrix of FIG. 2)shows a “knee” or inflection point beyond which the curve flattens inthe direction of increasing value of the given independent processvariables P, T and (A/B)_(solution). By operating at or in the vicinityof the knee point, the superior PZT material of the invention isproduced. The “vicinity” of the knee point will vary with theindependent process variable; in the case of the solution A/B ratio andpressure, the vicinity is preferably within ±25% of the knee point, andfor the temperature, the vicinity is preferably within ±5% of the kneepoint.

[0087] For the specific data shown in FIG. 2, this “knee” point is 1.02for the solution A/B ratio, 1750 millitorr for the deposition pressure,and 575° C. for the deposition temperature. By selection of theseindependent variable values, the corresponding dependent valuesproducing the superior PZT material of the invention produced with suchA/B solution ratio, pressure and temperature may be readily determined,including a Log J_(avg) center value of −4.35 amperes per squarecentimeter at operating voltage, Log Javg edge value of −6.77 amperesper square centimeter at operating voltage, a P_(sw) edge value of 35.1μC per square centimeter, a P_(sw) center value of 33.7 μC per squarecentimeter, and an atomic % Pb of 52.3%.

[0088] The present invention thus encompasses a “plateau effectdetermination” comprising the steps of establishing a correlativeempirical matrix of plots of each of ferroelectric polarization, leakagecurrent density and atomic percent lead in PZT films, as a function ofeach of temperature, pressure and liquid precursor solution A/B ratio,wherein A/B ratio is the ratio of Pb to (Zr+Ti), and identifying fromthe plots the “knee” or inflection point of each plot as defining aregion of operation with respect to the independent process variables oftemperature, pressure and liquid precursor solution A/B ratio, andconducting the MOCVD process at a corresponding value of thetemperature, pressure and liquid precursor solution A/B ratio selectedfrom such region of operation, as hereinafter described.

[0089] Set out in Table B below is a tabulation listing of the mostpreferred material properties (Type 2 properties) of thethickness-scalable and dimensionally-scalable PZT material of theinvention, wherein t is the film thickness of the PZT material, and 1 isthe effective lateral dimension, defined as side of a square with anarea that is the same as the capacitor area. TABLE B Basic ThicknessLateral property Scaling (t) dimension scaling (l) FerroelectricP_(SW) > 40 μC/cm² for t > 90 nm P_(SW) > 30 for 1 > 1 μm polarizationP_(SW) > 30 μC/cm² for t > 50 nm P_(SW) > 20 for 1 > (P_(SW)) P_(SW) >20 μC/cm² for t > 20 nm 0.05 μm Coercive E_(c) < 100 kV/cm for t > 50 nmE_(c) < 100 kV/cm for 1 > E-field E_(c) < 150 kV/cm for t > 20 nm 0.05μm (E_(c)) Leakage J < 10⁻⁵ A/cm² for t > 90 nm J < 10⁻⁴ A/cm² current J< 10⁻⁴ A/cm² for t > 50 nm for 1 > 0.05 μm density (J) Retention <3%/natural log decade (time in < 3%/natural log de- hours) at 150° C.,for t > 50 nm cade (time in hours) at 150° C., for 1 > 0.05 μm Cyclingfatigue < 10% decrease after 10¹⁰ cycles < 10% decrease after P_(SW) fort > 50 nm 10¹⁰ cycles for < 10% decrease after 10⁸ cycles 1 > 0.05 μmfor t > 20 nm

[0090] The invention contemplates the use of the “plateau effect” toachieve ferroelectric properties with the scaling properties specifiedin Table B, as well as the use of nucleation/smoothness methods toachieve ferroelectric properties with the scaling properties that arespecified in Table B.

[0091] The ferroelectric PZT material of the invention thus is adimensionally scalable material, and suitably comprises at least one ofthe Table A and/or Table B properties. The ferroelectric PZT material ofthe invention is also E-field scalable and pulse length scalable incharacter.

[0092] The PZT material of the present invention may be used to formcapacitive structures such as FeRAM devices, as well as othermicroelectronic devices and precursor structures in which PZT may beused to advantage. The invention thus contemplates the provision of amicroelectronic device structure including the PZT material of theinvention, e.g., a pulse length scalable PZT material of the inventionin combination with a power supply and associated power circuitryincluding such PZT material, as a microelectronic structure arranged forexcitation of the PZT material, wherein the excitation is characterizedby an excitation (voltage) pulse length in the range of from 5nanoseconds to 200 nanoseconds.

[0093] By way of example, the PZT material may be used to fabricate aferroelectric capacitor device structure, by forming a ferroelectricstack capacitor comprising a PZT ferroelectric material of the presentinvention as a capacitor element on a substrate containing buriedtransistor circuitry beneath an insulator layer having a via thereincontaining a conductive plug to the transistor circuitry. Suchfabrication process may comprise the steps of patterning, deposition,etch, diffusion, ion implantation, ion bombardment, chemicalmodification, etc.

[0094] A more complete understanding of the present invention is enabledby the following detailed description, including specific reference toan illustrative device structure comprising a PZT material according tothe invention.

[0095] Referring now to FIG. 3, there is shown the cross-section of anintegrated circuit semiconductor device 200, which is in the process offabrication. Device 200 includes a semiconductor substrate 202 that mayinclude active device structures, not shown, and an insulator layer 204.The semiconductor substrate 202 may be silicon, doped silicon, oranother semiconductor material. The insulator layer 204 is deposited onthe substrate 202 by any suitable deposition process. The insulatorlayer 204 may be, for example, silicon dioxide, silicon nitride, or somecombination thereof.

[0096] A conductive diffusion barrier layer 210, such as titaniumaluminum nitride TiAlN is deposited over the insulator layer 204. Alayer of conductive material 212, such as iridium, iridium oxide,platinum or combinations thereof, is deposited over the conductivediffusion barrier layer 210. Next, a layer of high dielectric constantmaterial 214, such as PZT, is deposited by MOCVD over the conductivelayer 212. A second layer of conductive material 216, such as iridium,iridium oxide, platinum, or combinations thereof, is shown depositedover the layer of high dielectric constant material 214.

[0097] A diffusion barrier material such as titanium aluminum nitride(TiAlN) will substantially reduce the possibility of diffusion of oxygenduring subsequent processing steps that require high temperatures inexcess of 500° C. Other materials can be used for the diffusion barrier,such as those disclosed in U.S. patent application Ser. No. 08/994,089filed Dec. 19, 1997 in the names of Peter S. Kirlin, et al., thedisclosure of which hereby is incorporated herein by reference in itsentirety.

[0098]FIG. 3 shows the portion of the device 200 after the device hasbeen patterned with photoresist and etched. Desired portions of theconductive diffusion barrier layer, upper and lower layers of iridium orother conductive material and of the high dielectric constant materialare left to form the upper electrode 216, capacitor dielectric 214,lower electrode 212, and lower electrode barrier layer 210.

[0099] A layer of interlevel dielectric 218 such as silicon dioxide orsilicon nitride, is deposited over all. The layer of interleveldielectric is patterned with photoresist and etch to form contact plugholes 221, 222, and 223. The insulator is etched down at the contractplug hole locations 221 and 222 until the iridium or other conductor ofthe lower electrode 212 and the upper electrode 216, respectively, arereached. Similarly the contact plug hole 223 is etched down through theinsulator layers 218 and 204 until the semiconductor substrate isreached. Once the contact plug openings are prepared, the device 200 isready for deposition of a layer of oxidation-barrier material.

[0100]FIG. 3 shows the semiconductor device 200 following an overalletch of the diffusion barrier layer leaving a diffusion barrier layer232 in contact with the lower capacitor electrode 212, a diffusionbarrier layer 234 in contact with the upper capacitor electrode 216, anda diffusion barrier layer 236 in contact with the semiconductorsubstrate 202. A transfer transistor of the memory cell may be locatedbelow the diffusion barrier layer 236, but it is not shown. As analternative to the aforementioned diffusion barrier deposition scheme,the barrier layers 232, 234, and 236 could be deposited as a singlecontinuous layer prior to the capacitor stack etch and deposition ofinsulating layer 218. According to this alternative configuration, thebarrier layer could be patterned and used as a hardmask for thesubsequent patterning of the capacitor stack. The alternate process flowwould continue with the deposition and patterning of the insulatinglayer 218.

[0101] A conductive material, or metallization, is deposited over theinterlevel dielectric 218 and the diffusion barrier layers 232, 234, and236. The conductive material 238 makes contact with the diffusionbarrier layers 232, 234, and 236. The conductive material 238 may beselected from a group of conductive materials such as aluminum, aluminumalloys, tungsten, tungsten alloys, iridium, and iridium alloys. Thediffusion barrier layers 232, 234, and 236 significantly reduce thepossibility of any diffusion of the layer of conductive material 238 tothe capacitor electrodes 212 and 216 of the semiconductor substrate 202.

[0102]FIG. 3 shown the semiconductor device 200 after the layer ofconductive material 238 is patterned and etched to form desired leadlines in the layer of conductive material. The pattern is formed ofphotoresist material. Etching is accomplished in accordance withwell-established practices known to those of ordinary skill in thesemiconductor manufacturing arts.

[0103] A layer of passivation dielectric 240 is deposited over theconductive material layer 238 and the interlevel dielectric 218. Thepassivation dielectric may be a material such as silicon dioxide,silicon nitride, or other insulator that can provide mechanical andelectrical protection for the top surface of the semiconductor device.Material of the passivation dielectric layer 240 is deposited bywell-known techniques.

[0104] The invention contemplates as an aspect thereof a microelectronicdevice structure comprising a PZT material of the present invention.While the invention has been describe herein with reference to specificfeatures, aspects and embodiments, it will be appreciated that theutility of the invention is not thus limited, and that the inventioncontemplates variations, modifications and embodiments other than thoseshown and described herein. The aforementioned capacitor geometry maycomprise a recessed capacitor geometry, for example, or other structuresand conformations that will be readily apparent to those with ordinaryskill in the art. Accordingly, the invention is to be broadlyinterpreted and construed to encompass all such variations andmodifications.

[0105] The features and advantages of the invention are more fully shownwith respect to the following illustrative examples.

EXAMPLE 1

[0106] The lead precursor chosen was leadbis(2,2,6,6-tetramethyl-3,5-heptanedionate) [Pb(thd)₂]. This compoundhas no appreciable vapor pressure at room temperature, which makes itmuch safer to handle than tetra-alkyl lead reagents. However, the lowvolatility of Pb(thd)₂ (0.05 Torr at 180° C.) requires the use of liquidprecursor delivery. Titaniumbis(isopropoxide)bis(2,2,6,6-tetramethyl-3,5-heptanedionate)[Ti(O-i-Pr)₂(thd)₂] was used as the titanium precursor. Zirconiumtetrakis(2,2,6,6-tetramethyl-3,5-heptanedionate) [Zr(thd)₄] was used asthe Zr source reagent. These compounds are extremely soluble in organicmedia and no possible detrimental ligand exchange occurs since thetitanium atom is coordinatively saturated.

[0107] The following process conditions were applied: OperatingParameter Process Condition Substrate temperature 550˜610° C. Bottomelectrode Ir/SiO₂/Si Total reactor pressure 1˜10 Torr Reactor walltemperature ˜210° C. Carrier Ar flow ˜200 sccm O₂ flow 500 sccm N₂O flow500 sccm Total reagent solution concentration 0.29 M Reagent solutionflow rate 0.1˜0.2 ml/min

[0108] In a representative run, the film was deposited at 565° C. onIr/SiO₂/Si. The pressure was 1.2 Torr, the oxidizer flow was a mixtureof 500 sccm O₂ and 500 sccm N₂O, and the reagent flow rate was 0.14ml/min for 32.5 minutes. XRF analysis gave the following thickness andcomposition data for the resulting PbZrTiO₃ film: Thickness (μm) Pb(at.%) Zr (at.%) Ti (at.%) 0.13 52.0 23.0 25.0

EXAMPLE 2

[0109] Solutions with a range of different Pb/(Zr+Ti) ratios were usedover a series of deposition runs. This ratio is hereafter defined as(A/B)_(g), denoting the conventional assignment of Pb to the “A” site,and Zr and Ti each to the “B” site in the perovskite cell, ABO₃. Thesubscript g denotes the gas-phase concentration in the reaction chamber,while (A/B)_(f) denotes the equivalent ratio in the film.

[0110] The gas phase ratio of Zr/(Zr+Ti) was held constant at 0.612.Under the conditions given above in Example 1 and for the specific CVDreactor employed, the gas phase ratio of Zr/(Zr+Ti)=0.612 resulted infilms with Zr/Ti˜40/60, which for bulk materials yielded a tetragonalcrystal structure and ferroelectric properties. This is a commoncomposition chosen for FeRAM applications because of its high P_(r) andthe relative ease in forming the perovskite phase for lower Zr/Tiratios.

[0111] Next, a series of PZT films was deposited with fixed depositiontime, under the process conditions set out in Table 1 below; the effecton (A/B)_(f) of (A/B)_(g) determined in this empirical work is shown inFIG. 1. Nominal film thickness was 100 nm. For low (A/B)_(g), (A/B)_(f)increased monotonically with mole fraction of lead in the gas phase.Over the range 0.93<(A/B)_(g)<1.53 a plateau was observed in (A/B)_(f),in the range of 1.10 to 1.15. For these films the perovskite phase wasthe only crystalline phase present.

[0112] The appearance of this processing window, where film compositionis insensitive to changes in the composition of Pb in the gas-phase, isrationalized in term of two competing processes: the formation ofperovskite PZT via decomposition of Pb, Zr and Ti precursors, and thedesorption of excess PbO from the growth surface. While we do not wishto be bound by any theory or mechanism in explanation for thisprocessing window, it is hypothesized that the vapor pressure of PbOover PZT is significantly lower than it is for solid PbO, as is the casewith bulk PZT (see the compiled bulk PZT material properties identifiedin K. H. Hartl and H. Rau, Solid State Comm., 7, 41 (1969)). TABLE 1 CVDdeposition conditions Precursors Pb(thd)₂, Zr(thd)₄, Ti(O-i-Pr)₂ (thd)₂Solution molarity 0.29 M Liquid flow rate 0.14 ml/min Substratetemperature 550° C. Pressure 1.2 torr Deposition rate 3.5 nm/minSubstrate Ir/MgO/SiO₂/Si

[0113] Under process conditions in which the kinetics of PZT formationare fast, and PbO volatility is high, single-phase, stoichiometric PZTcan be formed.

[0114] The presence of the plateau at (A/B)f values exceeding 1.00 maybe influenced by inaccuracy in the XRF measurement or by excess Pbdiffused into the bottom electrode. Analysis of incorporationefficiencies for the metallic constituents revealed a decrease in Pbefficiency for (A/B)_(g)>0.83, while Zr and Ti efficiencies remainednearly constant over the same range. This is consistent with theappearance of the plateau, and the absence of PbO from XRD analysis ofthe films. Film thickness decreased slightly with increased (A/B)g. Thiscorresponded to an approximate growth rate decrease from 3.8 to 3.2nm/min.

[0115] The as-deposited films were all smooth, dense, and fine-grained.The roughness and grain size values calculated from these images aregiven in Table 2 below. The measured film roughness was insensitive togas phase composition and was approximately double the starting surfaceroughness of the Ir films used as substrates.

[0116] With increasing (A/B)_(g), the grain size increased as did theextent of faceting, suggesting an enhanced surface mobility. This isbelieved to be a consequence of the higher PbO surface coverage thatmust be present during growth at higher gas-phase Pb concentrations ifthe previously described growth model is valid. The faceting in thehigh-Pb sample revealed predominately square features indicative of thepresence of PZT (001)-type orientations, a conclusion also supported bythe x-ray diffraction results. TABLE 2 Summary of AFM data forPZT/Ir/MgO layers. Film thickness is nominally 100 nm. (A/B)_(g)(A/B)_(f) RMS roughness (nm) Grain size (nm) 0.631 0.59 6.6 67 0.7310.97 8.4 72 0.831 1.01 7.8 86 1.031 1.08 7.7 91

[0117] X-ray diffraction analysis revealed single perovskite phase forfilms deposited with (A/B)_(g)≧0.83. For (A/B)_(g)<0.83, an additionalpeak was observed at 2Θ=29.9°. The intensity of this peak decreased withincreasing (A/B)_(g) and was attributed to formation of the undesirablepyrochlore phase under lead-deficient deposition conditions.

[0118] PZT films on Ir/MgO displayed dominant (001) and (101) PZTorientations; furthermore, the (001)/(101) ratio of PZT peak intensitiesincreased with increased (A/B)_(g), i.e., oriented toward the tetragonalc-axis with a c-axis lattice constant of 0.406 nm. No appreciable (111)PZT texture was observed on Ir/MgO. X-ray diffraction of the as-receivedsubstrates revealed principally (111) oriented Ir; however, aconsiderable (200) Ir peak was present.

[0119] The best electrical properties were found for films with(A/B)_(g) just above the knee in the curve shown in FIG. 1. Films withmuch higher or much lower (A/B)_(g) were electrically shorted. For 3Voperation, the remanent polarization (2P_(r)) and coercive voltage(V_(c)) were measured to be 85 μC/cm² and 0.77 V, respectively, for a150 nm thick film deposited at (A/B)_(g)=0.93. This high value ofremanent polarization is attributable to the strong preferred (001)orientation and the high degree of crystallization obtained on the Irsubstrate.

EXAMPLE 3

[0120] A central-composite-design experiment was used to probe a largevolume of process space and assess interactions between principalprocess variables. Deposition temperature (550, 575, 600° C.) andpressures (500, 1750, 3000 mTorr) were independently varied at fivedifferent values of (A/B)_(g): (0.53, 0.73, 0.93, 1.13, 1.53). Aconstant deposition time of 1660 seconds was used.

[0121] Compositionally, a plateau onset in (A/B)_(f) was observed at(A/B)_(g)=0.93. For a given pressure, film lead content was observed todecrease with increased deposition temperature. Furthermore,incorporation efficiencies of both lead and titanium decreased withincreasing (A/B)_(g) for all temperatures.

[0122] Electrically, the best samples arose from the conditions at thecenter of the design (575° C., 1.75 Torr, (A/B)_(g)˜1). Most of the goodsamples displayed a (−) voltage offset. There was no appreciablecenter-to-edge (wafer) effect. Leakage seemed to behave better for lowerPb and for thicker samples (˜130 nm up to ˜2.5 V).

EXAMPLE 4

[0123] Alternative zirconium oxide precursors are required, which aremore volatile than Zr(thd)₄ and which also have lower thermal stabilityto be more compatible with the surface decomposition of Pb(thd)₂, forexample.

[0124]FIG. 4 shows comparative TGA data for Pb(thd)₂, Ti(O-i-Pr)₂,(thd)₂and two selected Zr compounds: Zr(thd)₄ and Zr(O-i-Pr)₂(thd)₂. Althoughthe Zr(O-i-Pr)₂(thd)₂ compound possesses an undesirable residualscontent of nearly 20% at 400° C., it possesses a desirable thermalstability match with the Pb and Ti compounds commonly used for MOCVDPZT.

[0125] MOCVD PZT depositions were conducted on standard Ir/TiAIN bottomelectrodes (BEs) using the novel Zr(O-i-Pr)₂(thd)₂ (Zr-2-2) compoundwith a vaporizer temperature set to 200° C. Additional depositions wereprocessed using the standard Zr(thd)₄ (Zr-0-4) compound at a vaporizertemperature of 203° C. All other deposition conditions were heldconstant. Following PZT deposition, Pt top electrodes (TEs) were e-beamevaporated, and the samples were annealed at 650° C. in flowing argonfor 30 min.

[0126] Composition and electrical data for the Zr-2-2 samples arepresented along with data collected from the Zr-0-2 samples. The Zr-2-2samples, though appreciably lower in Pb and Zr content than the Zr-0-4samples, were electrically comparable.

[0127] In addition to the Zr(O-i-Pr)₂(thd)₂ precursor, MOCVD PZT may beprepared using still other novel Zr source precursors. For example,Zr₂(O-i-Pr)₆(thd)₂ has good ambient stability, high volatility andexcellent thermal compatibility with Pb and Ti precursors. TABLE 3Composition and electrical data for MOCVD PZT films deposited usingZr(O-i-Pr)₂(thd)₂ and Zr(thd)₄ Zr(O-i-Pr)₂(thd)₂ Zr(thd)₄ % Pb (at.%)49.5 ± 0.07 51.8 ± 0.12 Zr:(Zr + Ti) 0.322 ± 0.001 0.443 ± 0.008efficiency Pb  5.99 ± 0.049 7.43 ± 0.15 efficiency Zr  6.54 ± 0.078 4.36± 0.16 efficiency Ti  9.31 ± 0.035 10.7 ± 0.13 t (nm) 125 128 P_(SW)(μC/cm²) (2V)  36  38 ±J (A/cm²) (2V) 7.4 × 10⁻⁶; −1.5 × 10⁻⁶ < 3 × 10⁻⁶for both polarities

EXAMPLE 5

[0128] A number of samples are made up using PZT material formed inaccordance with the present invention. The samples are comprised ofbottom electrodes formed by sputtering techniques, deposition on theelectrodes of PZT material in accordance with the present invention,followed by deposition of top electrodes through a shadow mask by e-beamdeposition. The PZT deposition time was varied between 165 sec and 4065sec to target film a thickness between 10 nm and 260 nm.

[0129] Electrical testing of the samples provides electricalcharacteristics of the capacitor structures that validate the thickness,pulse length and area scaling properties, including ferroelectricpolarization, cycling fatigue, etc., of the ferroelectric PZT materialof the present invention.

[0130] Leakage current density versus E-field is given in FIG. 5. Thehigh “leakage” for the 77 nm film was directly confirmed. Thequalitatively different electrical behavior for films below a thicknessthreshold may be due to the high relative roughness(roughness/thickness), which results in some extremely thin regions inthinner films. Locally high E-fields are expected in those cases.Current density for the thicker films in the set (>77 nm) showedremarkably consistent E-field dependence. Leakage in both polarities wasin the 10⁻⁶ to 10⁻⁷ A/cm² range for 150 kV/cm. (150 kV/cm corresponds to1.9 V for the 125 nm film, for example.)

[0131] Leakage was one of four properties that was insensitive tothickness when plotted as a function of E-field; the other propertieswere coercive voltage (V_(c)), polarization saturation (P_(sw) versusV_(op)), and fatigue endurance.

[0132] The coercive voltage for each sample was determined from therelation 3V_(c)(measured)=V_(op) and the calculated values of E_(c)based on that method are given in FIG. 6. For PZT films greater than 77nm thick, E_(c) was approximately 50 kV/cm.

[0133] Pulse measurements were used to investigate polarizationsaturation. FIG. 7 shows the dependence of switched polarization onvoltage and E-field. The data shows the expected increase ofpolarization for higher voltages. Clear saturation behavior is seen forthe thicker films, which can withstand higher fields. For 125 mn andthicker films, saturated Psw>40 μC/cm². Normalized to P_(sw) nearsaturation (300 kV/cm), P_(sw) versus E is nearly independent of filmthickness. For all of the samples P_(sw) reaches nearly 90% of itmaximum value at 3E_(c)(˜150 kV/cm).

[0134] Fatigue properties for this sample set also displayed consistentproperties in terms of E-field scaling (FIG. 8). Fatigue measurementswere made at 150 kV/cm, which corresponds to 3E_(c). The fatiguewaveform was a square wave with a period of 10⁻⁵ seconds. Fatigue isnearly independent of PZT thickness with a reduction in P_(sw) by ˜50%at 10⁹ cycles.

[0135] Static imprint is manifested as an asymmetry in coercive voltage,and is defined as [V_(c)(−)+V_(c)(+)]/2. Imprint voltage was probed viarepeated measuring, poling, and annealing of a single capacitor.Following an initial measurement of V_(c)(+and −) at time=0; capacitorswere poled positive or negative to 2.5 V and then annealed at 150° C.(air) for 20 min. After cooling, the same (poled) capacitors werere-measured. Additional measurements were repeated following anneals of24 min. (i.e. 45 min. elapsed time) and 45 min. (90 min. elapsed time).

[0136]FIG. 9 show a semi-log plot of imprint voltage versus time. Thesamples had nearly identical imprint at time=0 (˜−0.1 V). It is evidentthe imprint increases significantly at some time prior to the firstmeasurement at 20 minutes. Thinner films were observed to have a lowerimprint rate than thicker films. This trend suggests analyzing the datain terms of an imprint E-field.

EXAMPLE 6

[0137] In order to simplify test equipment and sample preparation duringthe development of ferroelectric materials, electrical testing hastraditionally been conducted with pulse widths on the order of 1 mS andcapacitor areas on the order of 10⁴ μm². A disadvantage of this testingregimen is its inability to demonstrate the viability of electricalproperties at scales appropriate for devices (i.e. 25 nS pulses and 10²μm²). The market trend is toward devices that operate on increasinglyshorter time scales and with smaller capacitor areas, hence scalingissues will be critical to future device success.

[0138] The sample used for these measurements originated with a 6-inchdiameter Si wafer with an Ir bottom electrode, standard PZT, and a topelectrode that consisted of 40 nm of IrO₂ and 60 nm of Ir, as describedin Process Set A. Individual capacitors were defined using patternedphotoresist and reactive ion etching in a Cl₂/Ar/O₂ mixture. Followingpatterning the sample was annealed at 650° C. in flowing oxygen for 30min.

[0139] The test system consisted of an SRS DS345 arbitrary waveformgenerator, a Tektronix 620B digital storage oscilloscope, and a shuntresistor as shown in FIG. 10. Details of this testing protocol arefurther described in P. K. Larsen, G. Kampschoer, M. Ulenaers, G.Spierings and R. Cuppens, Applied Physics Letters, Vol. 59, Issue 5, pp.611-613 (1991). A standard square-pulse ferroelectric pulse train wasused. This pulse train consisted of one negative polarity pulse,followed by two positive pulses and two negative pulses (set, positive,up, negative, down). A typical drive signal, as measured at position Xin FIG. 10, and response signal as measured at position Y in FIG. 10,are shown in FIG. 11.

[0140] The total charge passing from the ferroelectric capacitor toground within each response pulse can be calculated from:

Charge: Q=(1/R _(s))∫V dV

[0141] Ferroelectric switching occurs when a ferroelectric capacitorthat has been previously poled by a negative (positive) pulse is poledup (down) by a subsequent positive (negative) pulse. Q_(sw) is definedto be the difference in total charge contained within a switching pulseand a non-switching pulse:

Q _(sw)=(S ₀ +S ₁)−(P ₀ +P ₁)

[0142] where S₀ and S₁ are the leading and trailing edge response pulsesfor the first switching pulse and P₀ and P₁ are the leading and trailingedge pulses for the first non-switching pulse (FIG. 11).

[0143] Measurements were made as described above with 1, 2 and 3 Vpulses and pulse lengths between 25 nS and 0.22 mS. The polarization wasfound to be independent of pulse length over the range investigated(FIG. 12).

[0144] Additionally, area scaling was investigated using 1 μS pulses andsquare capacitors from 33 μm×33 μm down to 4 μm×4 μm. Q_(sw) was alsofound to be independent of capacitor dimension over the rangeinvestigated (FIG. 13).

[0145] While the invention has been illustratively described herein withreference to specific aspects, features and embodiments, it will beappreciated that the utility and scope of the invention is not thuslimited and that the invention may readily embrace other and differingvariations, modifications and other embodiments. The invention thereforeis intended to be broadly interpreted and construed, as comprehendingall such variations, modifications and alternative embodiments, withinthe spirit and scope of the ensuing claims.

What is claimed is:
 1. A ferroelectric PZT material, having adimensionally scalable, pulse length scalable and/or E-field scalablecharacter.
 2. A ferroelectric PZT material having a dimensionallyscalable character.
 3. A ferroelectric PZT material having a pulselength scalable character.
 4. A ferroelectric PZT material having anE-field scalable character.
 5. A ferroelectric PZT material having adimensionally scalable character and a pulse length scalable character.6. A ferroelectric PZT material having a dimensionally scalablecharacter and an E-field scalable character.
 7. A ferroelectric PZTmaterial having a pulse length scalable character and an E-fieldscalable character.
 8. A ferroelectric PZT material, having adimensionally scalable, pulse length scalable and E-field scalablecharacter.
 9. The PZT material of claim 1, having a thickness of fromabout 20 to about 150 nanometers.
 10. The PZT material of claim 1,having a ferroelectric operating voltage below 2 Volts.
 11. Aferroelectric PZT material, having at least one of Type 1 properties.12. The PZT material of claim 11, wherein at least one of said Type 1properties includes a ferroelectric polarization PSW greater than 20 μCper square centimeter.
 13. The PZT material of claim 11, wherein atleast one of said Type 1 properties includes a leakage current density Jless than 10⁻⁵ amperes per square centimeter at a ferroelectricoperating voltage of the material.
 14. The PZT material of claim 11,wherein at least one of said Type 1 properties includes a dielectricrelaxation defined by J^(−n) log (time) wherein n is greater than 0.5.15. The PZT material of claim 11, wherein at least one of said Type 1properties includes a cycling fatigue defined by P_(sw) being less than10% lower than its original value after 10¹⁰ polarization switchingcycles.
 16. The PZT material of claim 11, having at least two of Type 1properties.
 17. The PZT material of claim 11, having at least three ofType 1 properties.
 18. The PZT material of claim 11, having all of saidType 1 properties.
 19. A ferroelectric PZT material having at least oneof Type 2 properties.
 20. The PZT material of claim 19, wherein at leastone of said Type 2 properties includes ferroelectric polarization,P_(sw).
 21. The PZT material of claim 19, wherein at least one of saidType 2 properties includes coercive E-field, E_(c).
 22. The PZT materialof claim 19, wherein at least one of said Type 2 properties includesleakage current density, J.
 23. The PZT material of claim 19, wherein atleast one of said Type 2 properties includes retention.
 24. The PZTmaterial of claim 19, wherein at least one of said Type 2 propertiesincludes cycling fatigue of ferroelectric polarization.
 25. The PZTmaterial of claim 19, having at least two of Type 2 properties.
 26. ThePZT material of claim 19, having at least three of Type 2 properties.27. The PZT material of claim 19, having at least four of Type 2properties.
 28. The PZT material of claim 19, having all of said Type 2properties.
 29. A ferroelectric PZT material having at least one of Type1 properties and at least one of Type 2 properties.
 30. A capacitorcomprising a ferroelectric PZT material according to any one of claims 1to
 29. 31. The capacitor of claim 30, having a capacitor area of fromabout 10⁴ to about 10⁻² μm².
 32. The capacitor of claim 30, wherein thePZT material is between a bottom electrode formed of a materialcomprising iridium and/or platinum, and a top electrode formed of amaterial comprising iridium and/or iridium oxide.
 33. The capacitor ofclaim 30, constituting a stack capacitor.
 34. A microelectronic devicestructure, comprising: a pulse length scalable ferroelectric PZTmaterial; and a power supply and associated circuitry arranged forexcitation of the PZT material, wherein the excitation is characterizedby an excitation (voltage) pulse length in the range of from 5nanoseconds to 200 nanoseconds.
 35. An FeRAM device, including acapacitor comprising a ferroelectric PZT material according to any oneof claims 1 to
 29. 36. The FeRAM device of claim 35, having a capacitorarea of from about 10⁴ to about 10⁻² μm².
 37. The FeRAM device of claim35, wherein the PZT material has a ferroelectric operating voltage below2 Volts.
 38. A method of fabricating a ferroelectric PZT film on asubstrate, comprising forming the film by liquid delivery MOCVD on thesubstrate under MOCVD conditions producing a ferroelectric PZT materialaccording to any one of claims 1 to
 29. 39. The method of claim 38,wherein the MOCVD conditions include use of a lead source reagentselected from the group consisting of Pb(thd)₂ and Pb(thd)₂pmdeta. 40.The method of claim 38, wherein the MOCVD conditions include use of azirconium source reagent selected from the group consisting of Zr(thd)₄and Zr(O-i-Pr)₂(thd)₂.
 41. The method of claim 38, wherein the MOCVDconditions include use of Ti(O-i-Pr)₂(thd)₂ as a titanium sourcereagent.
 42. The method of claim 38, wherein the MOCVD conditionsinclude use of Pb(thd)₂, Ti(O-i-Pr)₂(thd)₂ and Zr(thd)₄ as respectivelead, titanium and zirconium source reagents.
 43. The method of claim38, wherein the MOCVD conditions include use of Pb(thd)₂pmdeta,Ti(O-i-Pr)₂(thd)₂ and Zr(thd)₄ as respective lead, titanium andzirconium source reagents.
 44. The method of claim 38, wherein the MOCVDconditions include use of Pb(thd)₂pmdeta, Ti(O-i-Pr)₂(thd)₂ andZr(O-i-Pr)₂(thd)₂ as respective lead, titanium and zirconium sourcereagents.
 45. The method of claim 38, wherein the source reagents areprovided for liquid delivery MOCVD in a solvent medium comprising one ormore solvent species selected from the group consisting of:tetrahydrofuran, glyme solvents, alcohols, hydrocarbon solvents,hydroaryl solvents, amines, polyamines, and mixtures of two or more ofthe foregoing.
 46. The method of claim 38, wherein the source reagentsare provided for liquid delivery MOCVD in a solvent medium comprisingtetrahydrofuran:isopropanol:tetraglyme in an 8:2:1 volume ratio.
 47. Themethod of claim 38, wherein the source reagents are provided for liquiddelivery MOCVD in a solvent medium comprising octane:decane:polyamine ina 5:4:1 volume ratio.
 48. The method of claim 38, wherein the sourcereagents are provided for liquid delivery MOCVD in a solvent mediumcomprising octane:polyamine in a 9:1 volume ratio.
 49. The method ofclaim 38, wherein the source reagents are provided for liquid deliveryMOCVD in a solvent medium comprising tetrahydrofuran.
 50. The method ofclaim 38, wherein the substrate comprises a noble metal.
 51. The methodof claim 38, wherein the substrate comprises a noble metal selected fromthe group consisting of iridium, platinum, and combinations thereof. 52.The method of claim 38, wherein the substrate comprises a TiAlN barrierlayer overlaid by an iridium layer.
 53. The method of claim 38, whereinthe liquid delivery MOCVD includes vaporization of a source reagentsolution to form precursor vapor therefrom and flowing the precursorvapor to a CVD chamber in a carrier gas.
 54. The method of claim 53,wherein the carrier gas is selected from the group consisting of argon,helium and mixtures thereof.
 55. The method according to claim 38,further comprising flowing to the CVD chamber an oxidant mediumincluding at least one species selected from the group consisting of O₂,O₃, N₂O, and O₂/N₂O.
 56. A method of fabricating a ferroelectric PZTfilm on a substrate, comprising forming the film by liquid deliveryMOCVD on the substrate under MOCVD conditions including nucleationconditions producing a ferroelectric PZT material according to any oneof claims 1 to
 29. 57. A method of fabricating a ferroelectric PZT filmon a substrate, comprising forming the film by liquid delivery MOCVD onthe substrate under MOCVD conditions including temperature, pressure andliquid precursor solution A/B ratio determined by plateau effectdetermination from a correlative empirical matrix of plots of each offerroelectric polarization, leakage current density and atomic percentlead in PZT films, as a function of each of temperature, pressure andliquid precursor solution A/B ratio, wherein A/B ratio is the ratio ofPb to (Zr+Ti).
 58. A method of fabricating a ferroelectric PZT film on asubstrate, comprising forming the film by liquid delivery MOCVD on thesubstrate under MOCVD conditions including temperature, pressure andliquid precursor solution A/B ratio determined by plateau effectdetermination from a correlative empirical matrix of plots of each offerroelectric polarization, leakage current density and atomic percentlead in PZT films, as a function of each of temperature, pressure andliquid precursor solution A/B ratio, wherein A/B ratio is the ratio ofPb to (Zr+Ti), and wherein said ferroelectric PZT film comprises aferroelectric PZT material according to any one of claims 1 to
 29. 59. Amethod of fabricating a ferroelectric PZT film on a substrate,comprising forming the film by liquid delivery MOCVD on the substrateunder MOCVD conditions including Correlative Materials or ProcessingRequirements, to yield a ferroelectric PZT film having PZT Properties,wherein said Correlative Materials or Processing Requirements and PZTProperties comprise: PZT Properties Correlative Materials or ProcessingRequirements Basic properties: Ferroelectric polarization Film Pbconcentration > threshold level; P_(sw) > 20 μC/cm² operation on A/Bplateau above the knee region, and with temperature, pressure and gasphase A/B concentration ratio defined by plateau effect determinationLeakage current density Film Pb concentration within a J < 10⁻⁵ A/cm² atrange (between the minimum and operating voltage maximum) on the A/Bplateau, and with temperature, pressure and gas phase A/B concentrationratio defined by plateau effect determination Dielectric relaxationZr/Ti ratio < 45/55 For characteristic J^(−n) ∝ log Deposition P > 1.8torr (time), n > 0.5 and J < 1% ferroelectric switching current from0-100 ns. Retention Operation within ranges of temperature, Maintenanceof ferroelectric pressure and gas phase A/B properties (ferroelectricconcentration ratio defined by plateau domains) effect determinationAvoidance of cycling fatigue Use of Ir-based electrodes P_(sw) < 10%decrease after 10¹⁰ cycles E-field scalability Operation within rangesof temperature, pressure and gas phase A/B concentration ratio definedby plateau effect determination Surface smoothness Nucleation-growthconditions during film formation within ranges of temperature, pressureand gas phase A/B concentration ratio defined by plateau effectdetermination Grain size Nucleation-growth conditions during filmformation within ranges of temperature, pressure and gas phase A/Bconcentration ratio defined by plateau effect determination


60. A method of fabricating a FeRAM device, comprising forming acapacitor on a substrate including a ferroelectric PZT materialaccording to any one of claims 1 to 29, wherein the ferroelectric PZTmaterial is deposited by liquid delivery MOCVD under MOCVD conditionsyielding said ferroelectric PZT material.
 61. The method of claim 60,wherein the PZT material has a ferroelectric operating voltage below 2Volts.
 62. The method of claim 60, wherein the PZT film defines acapacitor area of from about 10⁴ to about 10⁻² μm².
 63. The method ofclaim 60, wherein the MOCVD conditions are determined by plateau effectdetermination.
 64. The method of claim 60, wherein the MOCVD conditionscomprise Correlative Materials or Processing Requirements, to yield aferroelectric PZT film having PZT Properties, wherein said CorrelativeMaterials or Processing Requirements and PZT Properties comprise: PZTProperties Correlative Materials or Processing Requirements Basicproperties: Ferroelectric polarization Film Pb concentration > thresholdlevel; P_(sw) > 20 μC/cm² operation on A/B plateau above the kneeregion, and with temperature, pressure and gas phase A/B concentrationratio defined by plateau effect determination Leakage current densityFilm Pb concentration within a range J < 10⁻⁵ A/cm² (between the minimumand maximum) at operating voltage on the A/B plateau, and withtemperature, pressure and gas phase A/B concentration ratio defined byplateau effect determination Dielectric relaxation Zr/Ti ratio < 45/55For characteristic J^(−n) ∝ log Deposition P > 1.8 torr (time), n > 0.5and J < 1% ferroelectric switching current from 0-100 ns. RetentionOperation within ranges of temperature, Maintenance of ferroelectricpressure and gas phase A/B properties (ferroelectric concentration ratiodefined by domains) plateau effect determination Avoidance of cyclingfatigue Use of Ir-based electrodes P_(sw) < 10% decrease after 10¹⁰cycles E-field scalability Operation within ranges of temperature,pressure and gas phase A/B concentration ratio defined by plateau effectdetermination Surface smoothness Nucleation-growth conditions duringfilm formation within ranges of temperature, pressure and gas phase A/Bconcentration ratio defined by plateau effect determination Grain sizeNucleation-growth conditions during film formation within ranges oftemperature, pressure and gas phase A/B concentration ratio defined byplateau effect determination